Simultaneous nitrification and denitrification in an aerobic biofilm biosystem with loofah sponges as carriers for biodegrading hydrolyzed polyacrylamide-containing wastewater

Optimization of synthetic domestic wastewater treatment performance in anoxic/aerobic sequencing batch reactor with zeolite addition

In this study, treatment performance was investigated based on chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), total inorganic nitrogen (TIN) and simultaneous nitrification and denitrification (SND) parameters in a zeolite-added anoxic/aerobic sequencing batch reactor. Response surface methodology (RSM) was used to model treatment performance, determine the impact of operating conditions, and optimize them. The effect of zeolite size, dosage and COD/NH4+-N (C/N) ratio as operating parameters were evaluated in the central composite design (CCD). Variance analysis (ANOVA) results of the quadratic model, high coefficients of determination and low values of the root mean square error (RMSE) for dependent variables indicated the validity of the model in predicting experimental results. The desirability function showed that optimum conditions were 0.80 mm for zeolite size, 3.05 g/L for zeolite dosage and 9.8 for C/N. Under these conditions, the maximum COD, NH4+-N, TIN removal efficiencies and SND efficiency were 92.85%, 93.3%, 77.33% and 82.96%, respectively. The results of the study showed that the most effective independent variable on dependent variables was the C/N ratio.

Study on potential microbial community to the waste water treatment from bauxite desilication process

Discharging waste water from the bauxite desilication process will bring potential environmental risk from the residual ions and organic compounds, especially hydrolyzed polyacrylamide. Characterization of the microbial community diversity in waste water plays an important role in the biological treatment of waste water. In this study, eight waste water samples from five flotation plants in China were investigated. The microbial community and functional profiles within the waste water were analyzed by a metagenomic sequencing method and associated with geochemical properties. The results revealed that Proteobacteria and Firmicutes were the dominant bacterial phyla. Both phylogenetical and clusters of orthologous groups' analyses indicated that Tepidicella, Paracoccus, Pseudomonas, and Exiguobacterium could be the dominant bacterial genera in the waste water from bauxite desilication process for their abilities to biodegrade complex organic compounds. The results of the microbial community diversity and functional gene compositions analyses provided a beneficial orientation for the biotreatment of waste water, as well as regenerative using of water resources. Besides, this study revealed that waste water from bauxite desilication process was an ideal ecosystem to find novel microorganisms, such as efficient strains for bio-desilication and bio-desulfurization of bauxite.

Partially hydrolyzed polyacrylamide: enhanced oil recovery applications, oil-field produced water pollution, and possible solutions

Polymers, such as partially hydrolyzed polyacrylamide (HPAM), are widely used in oil fields to enhance or improve the recovery of crude oil from the reservoirs. It works by increasing the viscosity of the injected water, thus improving its mobility and oil recovery. However, during such enhanced oil recovery (EOR) operations, it also produces a huge quantity of water alongside oil. Depending on the age and the stage of the oil reserve, the oil field produces ~ 7-10 times more water than oil. Such water contains various types of toxic components, such as traces of crude oil, heavy metals, and different types of chemicals (used during EOR operations such as HPAM). Thus, a huge quantity of HPAM containing produced water generated worldwide requires proper treatment and usage. The possible toxicity of HPAM is still ambiguous, but its natural decomposition product, acrylamide, threatens humans' health and ecological environments. Therefore, the main challenge is the removal or degradation of HPAM in an environmentally safe manner from the produced water before proper disposal. Several chemical and thermal techniques are employed for the removal of HPAM, but they are not so environmentally friendly and somewhat expensive. Among different types of treatments, biodegradation with the aid of individual or mixed microbes (as biofilms) is touted to be an efficient and environmentally friendly way to solve the problem without harmful side effects. Many researchers have explored and reported the potential of such bioremediation technology with a variable removal efficiency of HPAM from the oil field produced water, both in lab scale and field scale studies. The current review is in line with United Nations Sustainability Goals, related to water security-UNSDG 6. It highlights the scale of such HPAM-based EOR applications, the challenge of produced water treatment, current possible solutions, and future possibilities to reuse such treated water sources for other applications.

Hydrolyzed polyacrylamide biotransformation during the formation of anode biofilm in microbial fuel cell biosystem: Bioelectricity, metabolites and functional microorganisms

The anode biofilm serves as the core dominating the performance of microbial fuel cell (MFC) biosystem. This research provides new insights into hydrolyzed polyacrylamide (HPAM) biotransformation during the formation of anode biofilm. The current density, coulombic efficiency, voltage, power density, volatile fatty acid (VFA) production and total nitrogen (TN) removal enhanced with the thickening of biofilm (1-6 cm), and the maximums achieved 146 mA·m^-2, 47.3%, 8.76 V, 1.28 W·m^-2, 184 mg·L^-1 and 84.6%, respectively. HPAM concentration descended from 508 mg·L^-1 to 83.3 mg·L^-1 after 60 days. HPAM was metabolized into VFAs, N₂, NO₂^--N and NO₃^--N, thereby releasing electrons. Laccase and tyrosine/tryptophan protein induced HPAM metabolism and bioelectricity production. The microbial functions involving HPAM biotransformation and bioelectricity generation were clarified. The alternative resource recovery, techno-economic comparison and development direction of MFC biosystem were discussed to achieve the synchronization of HPAM-containing wastewater treatment and bioelectricity generation based on MFC biosystem.

A novel halophilic Exiguobacterium mexicanum strain removes nitrogen from saline wastewater via heterotrophic nitrification and aerobic denitrification

The utilization of halophilic bioresources is limited due to a lack of isolation and characterization work. A halophilic bacterium strain SND-01 of Exiguobacterium mexicanum was isolated in this study, which is the first report on its novel function in heterotrophic nitrification-aerobic denitrification (HN-AD). The strain SND-01 is slightly halophilic, surviving at 0 up to 9% (w/v) salinity. When utilizing ammonium, nitrate or nitrite as the sole nitrogen source in aerobic conditions, the isolated strain showed the maximum nitrogen removal rate of 2.24 ± 0.14 mg/(L·h), 3.63 ± 0.21 mg/(L·h) and 2.30 ± 0.23 mg/(L·h), respectively. Functional genes and key enzymes involved in heterotrophic-aerobic nitrogen transformations were characterized, establishing the pathway of HN-AD. The nitrogen removal via HN-AD is dependent on the C/N ratio, salinity and temperature. The halophilic Exiguobacterium mexicanum strain SND-01 shows a significant potential in biotreatment of saline wastewater in an easy and cost-effective way.

Key role of different levels of dissolved oxygen in hydrolyzed polyacrylamide bioconversion: Focusing on metabolic products, key enzymes and functional microorganisms

Dissolved oxygen (DO) played a short board effect on nitrogen biotransformation and pollutant metabolism. This study for the first time explored the key role of different levels of DO (covering anaerobic, anoxic and aerobic) on hydrolyzed polyacrylamide (HPAM) bioconversion. HPAM was metabolized to intermediates with different chain length. Volatile fatty acid (VFA) production rose first and then descended with DO concentration (0-2 mg·L-1), and the maximum reached 92.5 mg·L-1 when DO was 0.5 mg·L-1. Total nitrogen (TN) removal increased first and then dropped with DO concentration, and the maximum (61.4%) occurred at 0.5 mg·L-1 DO. NH4+-N dipped from 42.8 to 0 mg·L-1 and NO3--N rose from 0 to 32.8 mg·L-1 with DO concentration. The changes of enzyme activities were consistent with those of VFA production and TN removal, which were related to HPAM metabolism and N bioconversion. Microbial function was correlated to HPAM metabolism, N bioconversion and key enzyme.